This invention relates to the melting of glass and particularly to the use of bubblers to control the currents of molten glass in a melting furnace.
In a glass melting furnace of the continuous type a body of molten glass is maintained in the furnace and raw glass batch materials are fed through an inlet at one end of the furnace onto the surface of the pool of molten glass. There, the batch materials form an unmelted layer or "blanket" on the surface of the molten glass pool which may extend a considerable distance into the furnace until it becomes melted into the pool of molten glass. Heat for melting the batch is provided within the furnace by combustion burners above the level of the molten glass, sometimes aided by submerged electric heating means. At the opposite end of the furnace from the inlet end, melted glass is withdrawn from the pool of molten glass through an outlet opening.
The batch blanket at the inlet end of the melting furnace is relatively cold and acts as a heat sink and also shields the underlying portion of the molten glass pool from radiant heat from the overhead combustion. On the other hand, the region of the molten glass pool just downstream from the location where the batch blanket is melted tends to be the hottest region in the molten glass pool. These temperature conditions create two counter-rotating circulation cells in the molten glass pool. The tendency of the hot glass in the region just beyond the batch blanket to rise, and the tendency of relatively cool glass near the inlet end to sink, establish a circulation pattern beneath the batch blanket wherein glass in the upper portion of the pool beneath the blanket flows toward the inlet end (i.e., in the upstream direction) and glass in the lower portion of the pool under the batch blanket flows toward the outlet (i.e., in the downstream direction). Between the end of the batch blanket and the outlet end of the furnace the circulation pattern is in the opposite direction, with the surface portion of the glass flowing in the downstream direction and the glass near the bottom of the pool flowing in the upstream direction. At the juncture of these two convection cells a strong upwelling of molten glass is produced, and therefore this region is known as the "spring zone." The molten glass near the surface in the spring zone is typically the hottest portion of molten glass in the melting furnace and, therefore, it is desirable that the throughput stream of glass pass through this region to insure thorough melting and refining of the glass. However, this goal is not always attained because the spring zone effect may not be strong enough and because portions of the molten glass may bypass the spring zone. It is an object of the invention to improve the flow of glass through the high temperature regime of the spring zone.
It is well known to use bubblers in glass melting furnaces to agitate the molten glass and to control circulation patterns. Examples of bubblers in glass melting furnaces may be seen in U.S. Pat. Nos. 2,890,548 (Wright); 3,294,509 (Soubier et al.); 3,305,340 (Atkeson); 3,330,639 (Boettner et al.); 3,558,297 (Carney et al.). None of the known arrangements, however, provide the degree of flow control in and around the spring zone that is desired. Such an arrangement is provided by the present invention.